The invention relates to 3-tert-butylbenzaldehyde dimethyl acetal and to 3-tert-butyl-benzyl methyl ether and to an electrochemical method for producing 3-tert-butyl-benzaldehyde dimethyl acetal.
It is known to produce substituted benzaldehyde dimethyl acetals directly by electro-chemical methoxylation of the corresponding toluenes. P. Loyson, S. Gouws, B. Barton, M. Ackermann, S. Afr. J. Chem 2004, 57, 53-56 describe such a method. A disadvantage of the electrochemical side-chain methoxylation of toluenes is that only toluenes substituted with electron-pushing radicals such as tert-butyl, methyl or alkoxy can be methoxylated in economically interesting, yields. Although radicals such as ethyl, isopropyl or isobutyl likewise have an electron-pushing effect, their benzylic protons can likewise be substituted by methoxy groups in a secondary reaction during the electrochemical reaction. Thus, p-cymene cannot be methoxylated smoothly to give cuminaldehyde dimethyl acetal, as described in F. Vaudano, P. Tissot, Electrochimica Acta 2001, 46, 875-880, since the isopropyl group is always also proportionately methoxylated.
Substituted benzaldehyde dimethyl acetals and the aldehydes on which these are based are important intermediates, e.g. in the synthesis of 2-methyl-3-phenylpropanal fragrances such as e.g. cyclamen aldehyde, Lysmeral® (BASF SE) or silvial.
EP 0 129 795 A2 describes a method for producing substituted benzaldehyde dialkyl acetals by electrooxidation of correspondingly substituted alkyltoluenes in which an electrolyte is used which comprises 50 to 90% by weight of a corresponding alkanol, 8.5 to 40% by weight of the alkyltoluene and 0.01 to 1.5% by weight of an acid comprising HOBS groups.
EP 0 554 564 A1 discloses a method for producing substituted benzaldehyde acetals, where the substituents of the aromatic have at least one benzylic hydrogen atom, by electrochemical oxidation of a corresponding benzyl ether in the presence of a corresponding alkanol and also in the presence of an auxiliary electrolyte, by electrolyzing in the acidic, neutral or weakly basic range.
EP 0 638 665 A1 discloses a method for producing substituted benzaldehyde dialkyl acetals by electrochemical oxidation of correspondingly substituted toluene compounds by oxidizing a substituted toluene compound in the presence of an alkanol and of an auxiliary electrolyte in an electrolysis cell and relieving the reaction solution obtained in this way outside of the electrolysis cell to a pressure which is 10 mbar to 10 bar lower than the pressure in the electrolysis cell.
It was an object of the present invention to provide an electrochemical method for producing 3-tert-benzaldehyde dimethyl acetal which is characterized by a very good product yield, by a very good product selectivity and by a high current yield and at the same time can be carried out readily on an industrial scale using inexpensive starting materials and reagents and/or auxiliaries.